def detail(request, key): book = Book.get(key) tag_key_list = book.tags #tags is always not None tag_title_list = [] for tag_key in tag_key_list : try : tag_title = Tag.get(tag_key) if tag_title : tag_title_list.append(tag_title) except : pass return render_to_response('catalog/detail.html', {'book': book, 'tag_title_list': tag_title_list})